The institute of electrical and electronics engineers (IEEE) 802.16e standard was adopted in 2007 as a sixth standard for international mobile telecommunication (IMT)-2000 in the name of ‘WMAN-OFDMA’ by the ITU-radio communication sector (ITU-R) which is one of sectors of the international telecommunication union (ITU). An IMT-advanced system has been prepared by the ITU-R as a next generation (i.e., 4th generation) mobile communication standard following the IMT-2000. It was determined by the IEEE 802.16 working group (WG) to conduct the 802.16m project for the purpose of creating an amendment standard of the existing IEEE 802.16e as a standard for the IMT-advanced system. As can be seen in the purpose above, the 802.16m standard has two aspects, that is, continuity from the past (i.e., the amendment of the existing 802.16e standard) and continuity to the future (i.e., the standard for the next generation IMT-advanced system). Therefore, the 802.16m standard needs to satisfy all requirements for the IMT-advanced system while maintaining compatibility with a mobile WiMAX system conforming to the 802.16e standard.
Effective transmission/reception methods and utilizations have been proposed for a broadband wireless communication system to maximize efficiency of radio resources. An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference (ISI) with a low complexity is taken into consideration as one of next generation wireless communication systems. In the OFDM, a serially input data symbol is converted into N parallel data symbols, and is then transmitted by being carried on each of separated N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, and an interval of a transmitted symbol is increased, thereby minimizing inter-symbol interference.
When a system uses the OFDM as a modulation scheme, orthogonal frequency division multiple access (OFDMA) is a multiple access scheme in which multiple access is achieved by independently providing some of available subcarriers to a plurality of users. In the OFDMA, frequency resources (i.e., subcarriers) are provided to the respective users, and the respective frequency resources do not overlap with one another in general since they are independently provided to the plurality of users. Consequently, the frequency resources are allocated to the respective users in a mutually exclusive manner. In an OFDMA system, frequency diversity for multiple users can be obtained by using frequency selective scheduling, and subcarriers can be allocated variously according to a permutation rule for the subcarriers. In addition, a spatial multiplexing scheme using multiple antennas can be used to increase efficiency of a spatial domain.
Meanwhile, a wireless communication system employing a relay station (RS) has recently been developed. The RS is employed for cell coverage extension and transmission capability improvement. A base station (BS) provides a service to a mobile station (MS) located in a coverage boundary of the BS via the RS, and thus can obtain an effect of extending the cell coverage. In addition, the RS improves signal transmission reliability between the BS and the MS, thereby improving transmission capacity. Even if the MS is located inside the coverage of the BS, the RS may be used when the MS is located in a shadow area.
The RS can be classified into two types. First, a transparent RS is an RS which simply relays data transmitted from the BS to a subordinate RS or the MS while all information necessary for a relay process is determined by the BS. Second, a non-transparent RS is an RS which relays data by directly performing resource allocation, modulation and coding scheme (MCS) level determination, power control, or the like necessary for the relay process.
The RS may use a relay scheme, such as amplify and forward (AF) and decode and forward (DF). In the AF, the RS amplifies data transmitted from the BS and then delivers the data to the MS. In the DF, the RS identifies a destination station by decoding the data transmitted from the BS, and then relays the data to the destination station, i.e., the subordinate RS or the MS, by encoding the decoded data. Therefore, when using the DF, a delay time of data transmission increases along with the progression of a relay operation in a multi-hop relay environment in which a plurality of RSs constitute a layer.
Accordingly, there is a need for an effective data relay method.